Intermolecular and Intramolecular Friedel-Crafts Acylation of Carboxylic Acids using Binary Ionic Liquids: An Experimental and Computational Study

摘要

Traditional Friedel-Crafts acylation with acid halides suffers from waste byproducts such as SO2, HCl, and the hydrolysis of Lewis acid catalyst. Thus, the environmentally benign intermolecular and intramolecular Friedel-Crafts acylation of arenes with carboxylic acids as acylating agents has been investigated using a mixture of deep eutectic solvent and an ionic liquid as reaction media under microwave irradiation. The Friedel-Crafts acylations with carboxylic acids as acylating agents are challenging due to the low reactivity of carboxylic acids. In this paper, the desired products were obtained at moderate to good yields under microwave irradiation for a short reaction time. The Friedel-Crafts cyclization of 4-phenylbutyric acid is more effective than 3-phenylpropionoic acid under the present method. The reaction mechanism is proposed by combining experiments with density functional theory calculations, highlighting the critical role of ZnCl2, triflate anion (CF3COO-) in binary ionic liquids, and acidic conditions in accomodating a kinetic accessible pathway making the C-C bond.